This application claims the priority of Japanese Patent Application No. 2001-288183 filed on Sep. 21, 2001 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic endoscope apparatus, and more particularly, to contents of control of an electronic endoscope apparatus which is capable of reading stored charge obtained through one exposure by an image pickup element as 1-frame all pixel signals using a light shielding period set by a light shielding plate.
2. Description of the Related Art
In an electronic endoscope apparatus, light from a light source lamp is guided through a light guide to a tip of a scope and the light is irradiated from this scope tip onto an object under observation and an image of this object is captured by an image pickup element such as a CCD (Charge Coupled Device) via an objective optical system. This CCD reads signals (charge) stored every 1-field period one by one and forms a moving image. On the other hand, when a still image is formed, the CCD reads signals of all pixels obtained through exposure for 1 vertical scanning period taking advantage of a light shielding period.
FIG. 3 illustrates a light shielding plate drive period when the above-described still image is formed and the electronic endoscope apparatus uses a vertical sync signal of a {fraction (1/60)} sec period shown at the top of FIG. 3, for example. On the other hand, when a still image is formed, the light shielding plate is driven during a drive period which consists of a 1 vertical scanning period plus a 20.5H (H: horizontal scanning period) vertical blanking period as shown in the middle of FIG. 3, and in this way a light shielding period C is set as shown in the bottom of FIG. 3.
Then, during a light output period (exposure period) L at the bottom of FIG. 3, odd field signals in all pixel signals stored in the CCD are read during the above-described light shielding period C and even field signals are read during the next vertical scanning period of the light shielding period C, and in this way a still image is formed. According to this all pixel reading system, a still image is displayed on a monitor using all pixel signals obtained through exposure within a 1 vertical scanning period, and therefore this system has an advantage of obtaining clearer images without being affected by motions of an object under observation than when a moving image is formed.
However, since the conventional electronic endoscope apparatus needs to complete an operation from the start to stop of the above-described light shielding plate within a 1 vertical scanning period +20.5H, there is a problem that drive control over the light shielding plate is complicated.
FIGS. 4(A) to 4(D) show an operation from the start to stop of a rotating light shielding plate, and as shown in FIG. 4(A), a light shielding plate 1 is set in a position that will not block light source light (light path) 2 during the formation of a moving image. On the other hand, during the formation of a still image, once the light shielding plate 1 starts to rotate from this position, the light source light 2 can be completely shielded when the light shielding plate 1 moves to the position in FIG. 4(B) by an angle xcex81. On the other hand, when the light shielding plate is stopped, the light source light 2 can be completely shielded up to the position in FIG. 4(C) and the light source light cannot be completely shielded from this position to the position in FIG. 4(D), that is, the range of xcex82.
Furthermore, the start of the above-described rotating light shielding plate 1 is controlled for a short blanking period B1 (t1 to t2) of 20.5H (approximately 1.3 msec) shown in FIG. 3 and rotating the light shielding plate by the above-described angle 61 to completely shield the light source light during this period requires the torque for starting a motor that drives the rotation of the light shielding plate 1 to be increased. On the other hand, the stop of the light shielding plate 1 is also controlled for a short blanking period B2 (t3 to t4) of 20.5H and rotating the light shielding plate by the above-described angle xcex82 to completely stop the light shielding plate during this period requires brake control, etc. to give the motor a reverse potential. Thus, there is inconvenience that not only control of the light shielding plate 1 at the time of start and stop is complicated but also the circuit configuration is complicated.
The present invention has been achieved in view of the problems described above and it is an object of the present invention to provide an electronic endoscope apparatus capable of securing a control time at the time of starting and stopping the light shielding plate within an effective period of the vertical scanning period and driving the light shielding plate easily and with a simple circuit configuration.
In order to attain the above object, the present invention provides an electronic endoscope apparatus including an image pickup element that captures an image of an object under observation illuminated by light source light and a light shielding plate to shield the light source light, and capable of reading all pixel signals of the image pickup element taking advantage-of a period during which the light source light is shielded by this light shielding plate, characterized by including an image pickup element drive circuit that discharges the charge stored by the image pickup element during a predetermined period within an effective period after a blanking period of a vertical scanning period (during which image data can be retained) and performs control so as to set a non-operating period, and a light shielding plate drive circuit that performs drive control over the light shielding plate during a period including the non-operating period set by this image pickup element drive circuit.
Furthermore, another invention is characterized by reading, when a moving image is formed, charge stored from the image pickup element every 1 vertical scanning period as field signals without driving the light shielding plate and driving, when a still image is formed, the light shielding plate to read all pixels obtained through exposure within the 1 vertical scanning period as frame signals.
Furthermore, another invention performs electronic shutter control for controlling the charge storage time as a shutter speed after the control of the non-operating period and can thereby control the exposure time.
The above-described configuration provides a non-operating period within an effective period of the 1 vertical scanning period through discharge control over the stored charge of the image pickup element in the form of linking the non-operating period with a vertical blanking period. For example, if this non-operating period is set to 20H, it is possible to use a total period of 40.5H which is 20H plus a blanking period as the time to drive the light shielding plate both at the starting and stopping times. This gives an adequate margin of time for controlling the start and stop of the light shielding plate when all pixels are read and makes it easier to provide a completely shielded state and also simplifies the configuration for this purpose, too.